However I'm thinking of the solution which can be delivered at the lowest cost and implemented in the shortest possible timeframe.

A basic commuter rail service from Navan would need to be accompanied by a suite of complementary measures e.g. dedicated connecting buses from around the town (in any case the Navan town bus network is being redesigned in the near future).

In my view the main barrier to such a project is not financial but the will to actually do it; like most things rail related every conceivable project or idea will generate an artificially high price tag and a list of reasons to make it seem impossible.

Today it would not be possible to put the rail infrastructure in place that already exists around Navan, bridges, crossings, and even purchasing the line route. Despite this the authorities cannot come up with an imaginative idea of connecting up all this and making it accessible for commuters. The structure is already in place but the creativity and ideas are missing. Politicians in Ireland can only see new roads because there is a very powerful road building lobby that can influence the TDs but because rail is in public ownership there is less momentum. The people of Meath should insist on linking up the current infrastructure before it dissappears

While introducing Navan/Dublin commuter rail services via Drogheda is not the ideal option, a useful service could be established by investing a small fraction of what would be required to complete the line from Clonsilla.

The main requirement would be to upgrade the line to a sufficient standad to support up to 90 mph thus bringing the Navan to Drogheda jorney time down to 15 minutes or less. Navan trains could run limited stop beyond Drogeda, perhaps with a similar stopping pattern to the 0630 from Newry, but continuing to the Grand Canal Dock turnback. Journey time to Connolly of 55 to 65 minutes should be possible and would be sufficiently competive to attract business. Completion of the layout at Clongriffin would give some flexibility for faster trains to overtake the capacity hogging and slow moving DART trains.

This would be an interim measure to parially satisfy the demand for commuter rail services from Navan.

Services from Navan via Drogheda would involve more costs and complications than one might think. For a start, one would need lots of capacity enhancement between Drogheda and Dublin as it's already congested in places. Other possible projects such as an Airport link from Clongriffin and also the Interconnector already run up against constraints in the first 7 miles or so out of Connolly.

No doubt signalling improvements and plenty of options for two-way working would help, but South of Clongriffin there would be a need for 3 or 4 tracks (hugely costly because housing has been allowed close to the existing line).

Doesn't help if we have a Transport minister who is more fixated on law enforcement issues (breath tests, Sandyford Garda Station and judicial appointments) than on actual transport issues. Sorry to get political, but lack of real political will on public transport infrastructure is at the root of many problems, such as housing.

Costs have been put forward as issues with both the Cloncilla and Drogheda options from Navan but if you compared the costs of the motorways it would be only a fraction. The key is that the infrastructure is in place but not the political will. Look at the Phoenix park tunnel. CIE resisted its introduction for years pointing to a congested Connolly and signals difficulty. In modern cities trains are moving within minutes of each other but with modern control systems this is possible. Navan is already connected by rail but has no political punch to deliver - cost is not the issue its vision and will.

The demand is there but the strategic thinking is not in the Dáil where they are only keeping an eye on the next election fixing potholes. The rail infrastructure around Dublin and especially Navan rail link should be restored.

Is the alignment up from M3 Parkway in a good enough state that there's any significant financial benefit in using it?

I was wondering if a future airport line could be extended Ashbourne and Ratoath to join it near Dunshaughlin. It would mean a lot more significant population centres on the way to Navan than going entirely up the old alignment.